The present invention relates to a vinyl chloride resin composition with improved thermal deformation resistance, impact strength and processability.
As is well known, formed products of vinyl chloride resins exhibit practical thermal deformation resistance at temperatures up to about 70.degree. C. but are not suitable for use at temperatures thereabove. Accordingly, there have been various attempts to raise the thermal deformation temperature of the formed vinyl chloride resin products as disclosed in Japanese Patent Publn. No. 24867/1970 and No. 18101/1973, but the resin compositions disclosed therein do not have satisfactory processability.
More particularly, in order to improve the thermal deformation resistance of vinyl chloride resins including those also comprising an impact strength modifier, Japanese Patent Publn. No. 24867/1970 proposes adding to a vinyl chloride resin a styrene/acrylonitrile/methyl methacrylate/.alpha.-methylstyrene copolymer, and Japanese Patent Publn. No. 18101/1973 discloses the addition thereto of an .alpha.-methylstyrene/methyl methacrylate/acrylonitrile copolymer. However, in order to obtain highly satisfactory thermal deformation resistance, it is necessary to add either of the copolymers in a quantity of not less than 10% (by weight, as in all percentages and parts set forth hereinafter), preferably not less than 20%. For this reason, the processability of these resin compositions is widely different from that of a composition consisting of a vinyl chloride resin and an impact strength modifier resin. (Since vinyl chloride resins, in general, have no satisfactory impact strength, it is conventional to add an impact strength modifier when these resins are used for purposes where impact strength is required, and impact strength modifiers are also utilized in the aforementioned two inventions.)
As will be apparent from the specific data in the examples set forth hereinafter, the compositions of the two inventions described above have larger die swells, especially when these compositions are subjected to extrusion molding, than the vinyl chloride/impact strength modifier resin composition. The two prior art compositions of the above cited publications have processabilities differing greatly from those of conventional vinyl chloride resin compositions and therefore cannot be practically used for the profile extrusion or pipe extrusion for which strict dimensional accuracy is required.